These conservation issues are part of marine conservation, and are addressed
in fisheries science programs.
There is a growing gap between how many fish are available to be
caught and humanity’s desire to catch them, a problem that gets
worse as the world population
grows.

Similar to other environmental
issues, there can be conflict between the fishermen who depend on fishing for their
livelihoods and fishery scientists who realise that if future fish
populations are to be sustainable
then some fisheries must reduce or even close.

The journal Science
published a four-year study in November 2006, which predicted that,
at prevailing trends, the world would run out of wild-caught
seafood in 2048. The scientists stated that
the decline was a result of overfishing,
pollution and other environmental factors
that were reducing the population of fisheries at the same time as
their ecosystems were being degraded. Yet again the analysis has
met criticism as being fundamentally flawed, and many fishery
management officials, industry representatives and scientists
challenge the findings, although the debate continues. Many countries, such
as Tonga, the
United
States, Australia and New Zealand, and international management bodies have taken
steps to appropriately manage marine resources.

Effects on habitat

Some fishing techniques also may cause habitat destruction.
Dynamite fishing and cyanide fishing, which are illegal in many
places, harm surrounding habitat. Bottom
trawling, the practice of pulling a fishing net along the sea
bottom behind trawlers, removes
around 5 to 25% of an area's seabed life on a single run. A
2005 report of the UN Millennium Project, commissioned by
UN Secretary-General Kofi Annan, recommended the elimination of
bottom trawling on the high seas by 2006 to protect seamounts and
other ecologically sensitive habitats.

In mid October 2006, U.S. President Bush joined other world leaders
calling for a moratorium on deep-sea trawling, a practice shown to often have harmful
effects on sea habitat and, hence, on fish populations.

Overfishing

Overfishing has also been widely
reported due to increases in the volume of fishing hauls to feed a
quickly growing number of consumers. This has led to the breakdown
of some sea ecosystems and several fishing industries whose catch
has been greatly diminished. The extinction of many species has
also been reported. According to an FAO estimate, over 70% of the
world’s fish species are either fully exploited or depleted.
According to Nitin Desai, Secretary General of the 2002 World Summit on Sustainable Development,
"Overfishing cannot continue, the depletion of fisheries poses a
major threat to the food supply of millions of people."

The cover story of the May 15, 2003 issue of the science journal
Nature – with Dr. Ransom A.Myers, an internationally prominent
fisheries biologist (Dalhousie University, Halifax, Canada) as the
lead author – was devoted to a summary of the scientific
information. The story asserted that, as compared with 1950 levels,
only a remnant (in some instances, as little as 10%) of all large
ocean-fish stocks are left in the seas. These large ocean fish are
the species at the top of the food chains (e.g., tuna, cod, among
others). However, this article was subsequently criticized as being
fundamentally flawed, although much debate still exists (Walters
2003; Hampton et al. 2005; Maunder et al. 2006; Polacheck
2006;Sibert et al. 2006) and the majority of fisheries scientists
now consider the results irrelevant with respect to large pelagics (the open seas).

Ecological disruption

Fishing may disrupt food webs by targeting
specific, in-demand species. There might be too much fishing of
prey species such as sardines and anchovies,
thus reducing the food supply for the predators. It may also cause
the increase of prey species when the target fishes are predator
species such as salmon and tuna. Fisheries can reduce fish stocks that cetaceans rely on for food.

By-catch

By-catch is the portion of the catch that is not the target
species. These are either kept to be sold or discarded. In some
instances the discarded portion is known as discards.

Possible remedies

Many governments and intergovernmental bodies have implemented
fisheries management policies
designed to curb the environmental impact of fishing. Fishing
conservation aims to control the human activities that may
completely decrease a fish stock or washout an entire aquatic
environment. These laws include the quotas on the total catch of
particular species in a fishery, effort quotas (e.g., number of
days at sea), the limits on the number of vessels allowed in
specific areas, and the imposition of seasonal restrictions on
fishing.

In 2008 a large scale study of fisheries that used individual transferable quotas
and ones that didn't provided strong evidence that individual
transferable quotas can help to prevent collapses and restore
fisheries that appear to be in decline.

Fish farming has been proposed as a
more sustainable alternative to traditional capture of wild fish. However, fish farming has been
found to have negative impacts on nearby wild fish. Further,
farming of predatory fish like salmon can
rely on fish feed that is based on fish
meal and oil from wild fish.

The environmental impact of recreational fishing may be alleviated
to some extent by catch and
release fishing.